1. Field of the Invention
This invention relates to a method for measuring the torque transmitted by the driving wheel of a cycle and in particular the driving wheel of a bicycle.
A further object of the invention is to provide a device for the practical application of said method.
The present invention is also directed to a cycle equipped with said device.
2. Description of the Prior Art
In a known device of the type indicated in the foregoing and already disclosed in French Pat. No. FR-A-2,394,790, a roller is applied under the pressure of a spring against the driving run of the drive chain of the bicycle. As the effort transmitted by the chain is higher, so the driving run of the chain tends to lift and compress the spring to a greater extent. There accordingly exists a rule of correspondence between the deflection of the spring and the effort transmitted by the driving run of the chain.
This device suffers from numerous disadvantages. Prominent among these are its substantial weight and the fact that it provides inaccurate indications by reason of parasites corresponding to vibrations of the chain during operation. The effort measured is the effort transmitted by the chain which, at equal value, can correspond to different torques on the driving wheel if the bicycle is equipped with a gear-changing device. Moreover, the known device introduces friction on the chain.
German Pat. No. DE 31 50 149 describes a bicycle equipped with a torque-measuring device in which the detection elements can be placed at different locations. However, except for examples of construction corresponding in all cases to localization of the detection elements at the hub of the driving rear wheel, the last-mentioned patent specification makes reference solely to the possibility of mounting a recording instrument on the pedals or pedal cranks or else on the drive chain or the elements associated with this latter (front drive sprocket or rear driven sprocket). However, the cited patent (No. DE 31 50 149) fails to provide any information on practical solutions which may be adopted in the different cases thus contemplated.
It is only in the case of localization at the hub of the driving wheel that the aforementioned patent specification makes any definite suggestions. However, the solutions contemplated are both complex and costly since they involve the use of a hub of special design having two separate portions, namely a "driving portion" and a "driven portion" between which an elastic coupling element can be interposed. The measuring system is provided with means for detecting relative angular positions of each of the two portions thus provided on the hub. However, by reason of the very close proximity of these two portions, the angular differences are of very small value, which does not make it possible to carry out accurate measurements.
For these reasons, the object of the present invention is to propose a method, a device and a cycle in which measurement of torque or of a quantity related to torque is performed in a simple and accurate manner without entailing any modification of certain constituent elements of the cycle itself.